The theft and hijacking of motor vehicles in South Africa and elsewhere in the world has recently increased at an alarming rate. This trend is likely to continue in the future. Most existing vehicle anti-theft systems are relatively ineffective, and are not of great assistance to law enforcement agencies. In the light of the greater burden being placed on law enforcement agencies as a result of escalating crime and violence, vehicle owners are being forced to adopt alternative methods for protecting their vehicles which do not rely solely on protection by the authorities.
The amount of money lost directly and indirectly as a result of vehicle theft and hijacking in South Africa is estimated at being over six billion Rands per annum. Vehicle insurers are consequently paying vast sums of money in compensation, giving rise to exorbitant premiums. As a result, only about 25% of the vehicles in South Africa are insured.
A number of vehicle protection networks have recently been developed. South African patent 89/0103 discloses a vehicle security system which includes a number of security stations positioned strategically within an area which is to be monitored, such as a parking lot.
The security stations each have a low-powered transmitter and a low-powered receiver. If the vehicle is stolen, the radio transmitter carried by the vehicle is automatically actuated. Once such a vehicle comes within the range of one of the security stations, the signal transmitted from the vehicle is detected by the receiver at the security station, which then transmits an initial signal to the vehicle, causing it to be immobilised. A further signal is transmitted from the security station to a base station for identifying the location of the security station.
Recently passed legislation forbids the remote immobilisation of a vehicle, thereby placing limitations on the effectiveness of the systems described in patent 89/0103. In addition, a large number of security stations need to be distributed over a particular area in order to cover that area effectively. The relatively high powered transmitters in the security stations add significantly to their costs.
South African patent 89/0287 describes a locating system using a stationary unit or a mobile transmitting unit situated in a police or emergency vehicle. At least three receiving stations at known locations receive and process a randomly modulated radio signal emanating from the mobile transmitting unit. The signal is then transmitted from the receiving station to a central processing facility. This central processing facility determines the arrival time differences of the same modulated signal at each of the receiving stations and uses the data to locate the transmitting unit. In this system, a common time mark signal is required for establishing a common time base. Furthermore, relatively sophisticated and accurate circuitry needs to be employed to pinpoint the transmitting unit on the basis of the calculated time differences.